Stephen Paddock, 64, opened fire with automatic weapons on some 22,000 people at the Route 91 Harvest concert from the 32nd floor of the Mandalay Bay Resort and Casino on Sunday at around 10.30 p.m.

Paddock killed himself as special response team officers broke into the hotel room, police said.

Lombardo told the media that the investigation is concentrated on four locations: the hotel room; the concert venue; Paddock’s home in Mesquite, Nevada, and another property in northern Nevada that also belonged to the shooter.

Besides the 10 guns found in the hotel room, police discovered 18 firearms, explosives and thousands of rounds of ammunition at the residence in Mesquite, a town 128 km north of Las Vegas.

Paddock also had ammonium nitrate, which can be used to make bombs, in his vehicle, the sheriff said.

Regarding the motive for the deadliest mass shooting in US history, Lombardo said that he could not “get into the mind of a psychopath”.

Paddock had not been flagged by any local, state or federal agency as a potential threat, the sheriff said.

The gunman’s roommate, Marilou Danley, was initially identified by police as a person of interest in the case, but authorities later said they did not believe she was involved in the shooting.

Lombardo said his office had learned that Danley is abroad, “apparently in Tokyo”.

President Donald Trump discussed the massacre during a brief address delivered at the White House, saying “it was an act of pure evil”.

Trump said that he plans to travel to Las Vegas on Wednesday to meet with law enforcement personnel and relatives of the victims.

Paddock’s brother, Eric, told US media outlets at his home in Central Florida that the shooting came as a complete surprise to him.

“I don’t understand. It doesn’t make sense,” Eric Paddock said.

Stephen Paddock lived in Melbourne, a city on Florida’s east-central Space Coast, until 2015, officials said.

“There’s nothing I can say. My brother did this. It’s like he shot us. I couldn’t be more dumbfounded,” Eric Paddock said.

Eric Paddock said he had not heard from his brother since last month, when Stephen texted him to see how the family had fared with hurricane Irma.

Hesaid that his and Stephen’s father was Benjamin Hoskins Paddock, a career criminal and convicted bank robber.

The Federal Bureau of Investigation, meanwhile, said it could not find any links between Paddock and foreign terrorist organisations.

“We have determined, to this point, no connection with an international terrorist group,” an FBI spokesman said in a press conference in Las Vegas.

“As this investigation continues, we will continue to work with our partners to ensure that this is factually, thoroughly and absolutely investigated, to be able to bring comfort and peace back to this community.”

Earlier on Monday, the Islamic State (IS) terror group claimed responsibility.

IS said in a statement, whose authenticity has not been verified, that the gunman was “a soldier of the Islamic State”.

Sheriff Lombardo said that it would take time to identify all of the victims.